Accurate assembly on a production line basis usually involves tooling to insure parts to be joined are accurately positioned relative to one another. For example, component parts may be located in a fixture for preliminary fastening thereby establishing correct alignment, after which the assembly can be manually or automatically secured at other locations. The tooling employed for the proper simultaneous positioning of workpieces is not readily adapted to different jobs. Thus, when a second combination of parts is to be assembled, new fixtures are ordinarily needed.
Since many industrial operations can be accomplished with robotics it might be supposed that simultaneous positioning of parts without the usual fixturing could be accomplished with a plurality of robots, e.g., one to position each component part. While proposals have been advanced for the joint use of robotic arms (for example, see Devol et al, U.S. Pat. No. 3,890,552, and Gallaher, Jr., U.S. Pat. No. 4,252,360), coordinated motion of plural robots is not well developed, especially where accurate movement is required with respect to a third device or machine tool. Problems arise because of programming complexity, inaccurate relative positioning to desired tolerance levels, and collision detection and avoidance. Therefore, accurate part assembly by this method has not proved practical for the present state of development of the robotics art. Furthermore, an important consideration simply relates to the expense of proliferating programmed robots.